1. Field of the Invention
The invention relates to a cement wallboard and, more specifically, to a lightweight cement wallboard having a smooth surface suitable for adhesion of tile to the board.
2. Description of the Related Art
Cementitious panels have long been used in commercial and residential construction projects. The boards are commonly screwed or nailed into a wall frame. Wallboards can be used in generally dry conditions without significant modification. The use of wallboards in wet or humid areas such as bathrooms or shower rooms present special challenges. The wallboards must be resistant or impervious to heat and moisture, and preferably can be used as a substrate for ceramic tiles.
Conventional gypsum wallboard panels are made from a wet slurry of calcium sulfate dihydrate (“gypsum”) sandwiched between two layers of paper. The slurry is allowed to set, affording a rigid wallboard. The wallboards are typically cut and dried in commercial ovens prior to packaging for sale or use.
Various designs of wallboards have been proposed to address the weight, strength, appearance, preparation price, or industrial applicability of the boards.
U.S. Pat. No. 3,312,585 suggests a gypsum wallboard containing a set gypsum core, paper enclosures, and a water impervious film adhered to the paper. The wallboard is suggested as being especially useful in bathtub enclosures, shower stalls, and other environments frequently contacted by water. The paper completely encloses the gypsum core. Organic synthetic polymeric thermoplastics (e.g. polyvinyl chloride) are preferred to prepare the adhered film.
U.S. Pat. No. 3,993,822 presents a multi-layer gypsum board containing a mixture of gypsum, water, and fibers. A composite coating of a fiberglass layer and a layer of fiberglass fleece is embedded into one face of the board. The opposing face can have a similar coating, or a pasteboard.
U.S. Pat. No. 4,298,413 suggests a process and apparatus for producing fabric-reinforced thin concrete panels. The components are deposited on a web of disposable carrier material such as polyethylene coated paper while moving on a conveyor belt. The produced concrete panels contain the disposable carrier material, a web of reinforcing fabric, a layer of cement, a core mix, a second web of reinforcing fabric, and a second layer of cement.
U.S. Pat. No. 4,617,219 offers a reinforced concrete structure containing a nonwoven fabric reinforcing material encapsulated in cement. The fabric extends throughout the whole structure, or multiple fabric layers can be used in a sandwich or composite type structure. The fabric can also contain a woven or nonwoven scrim to improve the strength of the structure.
U.S. Pat. No. 4,647,496 presents a water resistant fibrous mat-faced gypsum board. A gypsum core is sandwiched between two sheets of porous glass mat. The gypsum core can contain one or more additives to improve the water resistance of the board.
U.S. Pat. No. 4,948,647 describes a backer board to which ceramic tile can be bonded in a bathroom or shower area. The board is made by forming a gypsum core board with fiber glass laminated composite facings, which include an inner fiber glass scrim, an outer fiber glass nonwoven matte, and an acrylic film. The film is made of an acrylic latex.
U.S. Pat. No. 5,030,502 suggests a concrete construction panel having a layer of reinforcing mesh bonded to each face. The mesh is wrapped around the edge of the panel.
U.S. Pat. No. 5,221,386 suggests a cement board having a woven mesh of reinforcing fibers underlying the top, bottom, and longitudinal edge surfaces. The board is produced continuously on a conveyor belt.
U.S. Pat. No. 6,054,205 describes a glass fiber facing sheet comprising an open mesh glass scrim for use in cement boards. The facing sheet can be used on one or both faces of a cement board.
U.S. Pat. No. 6,187,409 B1 suggests a cement panel with reinforced edges. The longitudinal edges are reinforced with a network of fibers. The panels are relatively strong and hard, and allow nails or screws to be driven without the drilling of pilot holes.
U.S. Pat. No. 6,316,087 B1 describes a structural panel containing cement, vermiculite, and fibers. The fibers are used within the core of the panel to enhance lateral and surface integrity. The surface of the panel is coated with foil.
U.S. Pat. No. 6,368,024 B2 describes a geotextile fabric for use in reinforcing earthen retaining walls and related structures. The fabric inhibits soil movement in a direction perpendicular to the face of the structure.
U.S. Pat. No. 6,391,131 B1 offers a glass fiber facing sheet for cement boards that reduces the pitting associated with open mesh glass scrims. The facing sheet can be incorporated into a smooth cement board. A cement slurry is deposited onto a first glass fiber facing sheet, then a second glass fiber facing sheet is applied. A low viscosity cement slurry can be applied onto the surface of the second facing sheet.
U.S. Pat. No. 6,406,779 B1 describes a paperless gypsum/fiber board with at least one surface containing fully hydrated gypsum and reinforcing fiber. The surface is coated with a primer containing an aqueous emulsion of a film-forming polymeric material.
While the prior art discloses various improvements to boards, the need for a strong, lightweight, smooth, and easily scored/snapped board has not yet been met.